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[12] THE INTERCAFE CORMORANT MANAGEMENT TOOLBOX 4 CORMORANT MANAGEMENT TOOLS Limiting the interaction between cormorants and fish can be achieved in a number of ways, each falling into one of four broad categories of action: 1. Scaring cormorants away from a fishery. 2. Protecting the fish — by preventing cormorants from reaching them. 3. Altering fish availability to cormorants — by making a fishery less attractive as a foraging site. 4. Reducing overall cormorant numbers — for example, by killing cormorants locally to reinforce scaring at specific sites, killing them more intensively, or reducing their reproductive efficiency. In addition, under some circumstances cormorant-fishery conflicts can be addressed through the use of financial or other compensation measures. The Toolbox aims to summarise information on each category of action with regard to the methods available, their efficacy, the constraints on their deployment or use, and the relative costs. The aim is to provide a broad overview of the effectiveness of different management options for different cormorant-fishery conflict situations. 4.1 Scaring Cormorants Away From A Fishery The basic philosophy behind techniques to scare birds away from a fishery is that cormorants are startled sufficiently to move to another foraging site by means of auditory, visual or even chemical deterrents. Clearly, the effectiveness of these techniques relies on: (1) the deterrents being sufficiently frightening to cormorants to make them move elsewhere; and (2) there being a ‘better’ alternative site for them to move to. The main drawback of these techniques is that cormorants eventually (often quite quickly) realise that they offer no real threat and the birds become ‘habituated’ to the noises, sights or smells, ignoring them thereafter. However, there is good evidence that birds are scared consistently by human presence if they perceive that humans are associated with danger. Where this is not the case, the birds can sometimes be approached at close quarters and show no apparent fear of man. The key to the successful use of auditory and/or visual deterrents seems to be to make them as unpredictable as possible by changing their location and frequency of use, and by using a number of techniques in combination. If these deterrents are used in conjunction with highly- visible human presence, this will increase their overall efficacy but may reduce their cost-effectiveness. As with many other techniques, it seems best to operate these deterrents before or as soon as birds arrive at a site — thus preventing them from getting used to the area as a foraging site in the first place. Once birds have learned that a site is good for foraging or breeding, it will be much harder to deter them from coming to it. 4.1.1 Auditory deterrents A number of commercially produced noise-generating bird scarers are available — for example, through local agricultural suppliers. These vary considerably in their price and complexity, from simple humming tapes to relatively sophisticated, automatic devices such as gas cannons. A general consideration with all these devices is noise nuisance, and any national and local controls on their use must be taken into account. 4.1.1.1 Gas cannons Gas cannons are deterrent devices that produce loud banging noises by igniting a mixture of gas (either acetylene or propane) and air under pressure. The frequency of detonation can be regulated by adjusting the gas feed or with an

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Page 1: 4 CORMORANT MANAGEMENT TOOLS - European ...ec.europa.eu/environment/nature/cormorants/files/Page_12...4 CORMORANT MANAGEMENT TOOLS Limiting the interaction between cormorants and fish

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the intercafe cormorant management toolbox

4 CORMORANT MANAGEMENT TOOLS

Limiting the interaction between cormorants and fish can be achieved in a number of ways, each falling into one of four broad categories of action:

1. Scaring cormorants away from a fishery.

2. Protecting the fish — by preventing cormorants from reaching them.

3. Altering fish availability to cormorants — by making a fishery less attractive as a foraging site.

4. Reducing overall cormorant numbers — for example, by killing cormorants locally to reinforce scaring at specific sites, killing them more intensively, or reducing their reproductive efficiency.

In addition, under some circumstances cormorant-fishery conflicts can be addressed through the use of financial or other compensation measures.

The Toolbox aims to summarise information on each category of action with regard to the methods available, their efficacy, the constraints on their deployment or use, and the relative costs. The aim is to provide a broad overview of the effectiveness of different management options for different cormorant-fishery conflict situations.

4.1 Scaring Cormorants Away From A Fishery

The basic philosophy behind techniques to scare birds away from a fishery is that cormorants are startled sufficiently to move to another foraging site by means of auditory, visual or even chemical deterrents. Clearly, the effectiveness of these techniques relies on: (1) the deterrents being sufficiently frightening to cormorants to make them move elsewhere; and (2) there being a ‘better’ alternative site for them to move to.

The main drawback of these techniques is that cormorants eventually (often quite quickly) realise that they offer no real threat and the birds become ‘habituated’ to the noises, sights or smells, ignoring them thereafter. However, there is good evidence that birds are scared consistently by human presence if they perceive that humans are associated with danger. Where this is not the case, the birds can sometimes be approached at close quarters and show no apparent fear of man.

The key to the successful use of auditory and/or visual deterrents seems to be to make them as unpredictable as possible by changing their location and frequency of use, and by using a number of techniques in

combination. If these deterrents are used in conjunction with highly-visible human presence, this will increase their overall efficacy but may reduce their cost-effectiveness. As with many other techniques, it seems best to operate these deterrents before or as soon as birds arrive at a site — thus preventing them from getting used to the area as a foraging site in the first place. Once birds have learned that a site is good for foraging or breeding, it will be much harder to deter them from coming to it.

4.1.1 Auditory deterrents

A number of commercially produced noise-generating bird scarers are available — for example, through local agricultural suppliers. These vary considerably in their price and complexity, from simple humming tapes to relatively sophisticated, automatic devices such as gas cannons. A general consideration with all these devices is noise nuisance, and any national and local controls on their use must be taken into account.

4.1.1.1 Gas cannonsGas cannons are deterrent devices that produce loud banging noises by igniting a mixture of gas (either acetylene or propane) and air under pressure. The frequency of detonation can be regulated by adjusting the gas feed or with an

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the intercafe cormorant management toolbox

automatic timing device. Most cannons produce a single bang at pre-set, timed or random intervals, but some devices can produce double or triple bangs, and rotators are available so that the noise can be aimed in different directions. Some are regulated by computer to produce a random length of the volley and with random intervals between volleys, or they may incorporate light detectors to allow the device to be turned off at night.

A gas cannon is relatively expensive and prices vary, depending on whether it is electronic or mechanically ignited; whether it is a single, double or multi-bang device; and whether features such as a rotator or mechanical or electronic timer are fitted. The unexpected noise

produced by a cannon is similar to the noise of a shotgun and causes a startle reflex, thus prompting birds in the vicinity to take flight. Their efficacy is reportedly heightened where birds have had prior experience of shooting to kill.

Gas cannons are widely used throughout Europe at aquaculture facilities and to protect inland fisheries, particularly at smaller sites. They have also been deployed at specific locations or for particular times at larger sites — for example, to protect fishing gear (e.g. fixed nets), or to restrict local damage for short, highly sensitive periods. These might include the draining and harvesting of Common Carp (Cyprinus carpio) ponds, during aggregations of breeding or

migrating fish such as Atlantic Salmon (Salmo salar) smolts, or in the vicinity of obstructions or barriers in rivers that may cause fish to congregate and hence increase their vulnerability to predation.

The effectiveness of gas cannons depends on how they are used, the size of the site to be ‘protected’, and the availability of alternative feeding areas for the birds close by. Local conditions, such as wind direction and strength, can also affect the intensity of noise. Cannons are more cost effective at smaller fishery sites, and the cost of sufficient numbers to cover a large area may be prohibitive. Researchers have suggested that one cannon can protect 1.3–2.0 ha at aquaculture facilities, if

Gas cannon. Photo courtesy of Thomas Keller.

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reinforced with other techniques. A survey of catfish (Ictalurus spp.) farmers in the USA indicated varying levels of satisfaction with the use of gas cannons to deter Double-crested Cormorants: around 10% of respondents felt they were ‘highly effective’ and about half found them ‘somewhat effective’; others regarded them as ‘ineffective’.

A simple field experiment carried out in the Czech Republic recorded the reactions of cormorants to the firing of a gas gun. A number of cormorant responses were recorded: (a) no reaction; (b) taking fright; (c) diving; (d) soaring and circling; and (e) flying out of the pond. These were found to be correlated with the distance of the birds from the gas gun. Typically, birds up to 300 m away displayed an active response (e.g. soaring and circling, flying out of the pond), suggesting that this method would be particularly effective on smaller fish ponds.

The general consensus of opinion is that gas cannons are most effective when moved every few days, have variable firing intervals and are deployed in combination with other scaring techniques. For example, placing a cannon in a hide used by shooters, and frequently moving it between hides, may prolong the scaring effects of both the shooting and the cannon. Gas cannons employed at fish-rearing ponds in Israel have also been mounted on wheeled carriages or on vehicles to make them highly mobile, where their effectiveness is reinforced by human presence and shooting. Products are also available that combine visual and acoustic stimuli to scare birds — the ‘Rotating Hunter’ consists of two propane cannons and the metal silhouette of a person that swivels with the force of each bang.

The main reason for cannons losing their effectiveness is habituation — birds get used to the noise and are no longer scared

away by it, especially if they have no experience of shooting to kill. A cannon firing repeatedly without any variation in timing or direction quickly loses its potential to scare birds. In such circumstances, cormorants have even been reported to use gas cannons as perches. Although cannons can be effective if the firing frequency and direction are varied, these scarers may be socially unacceptable near residential areas due to public concern about noise nuisance, especially if left to fire at night. However, pointing cannons away from houses and constructing simple straw baffles around them allows the devices to be placed at approximately half the distance of cannons without baffles, with no increase in noise nuisance. As sounds tend to be heard at greater distance at night, gas cannons near human settlements should be turned off or programmed to stop at night, unless Night Herons (Nycticorax nycticorax) or other nocturnal birds are also a problem.

Vehicle-mounted gas cannon. Photo courtesy of Thomas Keller.

‘A cannon firing repeatedly without any variation in timing or direction quickly loses its potential to scare birds’

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Gas cannons may also have an undesirable effect on other wildlife (e.g. birds and mammals) and humans (e.g. fishermen or fish farm workers), and they may also need to be located in secure locations to guard against theft. One must also be aware that the cannon noise may be mistaken for gunshots, and it would be prudent to inform the police, wildlife rangers and, in some countries where they may be deployed near national borders, the military about their presence. It may also be wise to advertise the use of such equipment widely to anglers, or others using a site, as the loud report may be disturbing to those with a nervous disposition or certain medical conditions.

Moreover, in other circumstances the use of gas cannons may be imprudent. For example, at fish over-wintering ponds stocked with very large densities of small fish, the noise of cannons can agitate and stress the fish. At sites in Italy, such stress has reportedly caused fish to move, exposing them to more environmentally harsh conditions and leading to mass mortalities.

4.1.1.2 Pyrotechnics Pyrotechnic devices are widely used as a cormorant deterrent at aquaculture facilities and to protect inland fisheries, particularly at smaller sites. They produce loud bangs or whistles and emit flashes of light and colour, and they can provide a cheaper and more flexible alternative to gas cannons, depending on the level of use and whether their use introduces additional manpower costs.

There are a wide variety of noise-producing cartridges, including shell

crackers, screamer shells, whistling and exploding projectiles, bird bangers, flash/detonation cartridges and flares. These can be fired from modified pistols (with a range of approximately 25 m) or shotguns (range of 45–90 m) and can produce noise levels of up to 160dB. As the direction and intensity of firing can be controlled to suit the bird species and location, an advantage of this technique is that deterrence can be targeted and disturbance of non-target species minimised. Be aware that both the cartridges and the gun require a firearms certificate in some countries, and legal restrictions on their use may also apply. In some countries, pyrotechnic operators need to be licensed or carry special insurance.

Alternative pyrotechnics include bird-scaring rockets — similar to recreational fireworks — and rope-firecrackers. These devices are relatively inexpensive (for short-term use) and easy to use. The rope-firecrackers (‘banger ropes’)

also require little manpower — these are simply lengths of slow burning fuse with bangers inserted at intervals to produce a series of loud explosions at approximately 20-minute intervals. Placing them inside clean, empty oils drums can enhance the noise of the explosions, but particular care is needed to ensure this is done safely. Weather conditions can affect the burning speed of the rope and there is also a danger of creating a fire hazard. As with all pyrotechnics, great care must be taken with their storage and transport.

In Israel, some fishermen have been licensed to use professional fireworks and have also explored the use of remote-control devices to set off pyrotechnics placed at various locations around fish farms. Trials were completed with some success, but this approach was not adopted for widespread use due to the relatively high costs and some technical problems. A large variety of powerful fireworks are available, thereby helping to prevent bird habituation, and many are much less expensive than simple banger shells. However, legal restrictions on their use apply in most countries.

In a survey of Mississippi catfish farmers, 21 of 281 respondents (around 7%) regularly used pyrotechnics. Of these, 24% considered them to be ‘very effective’, 57% ‘somewhat effective’ and 19% ‘not effective’. Other researchers have reported variable effectiveness in the use of pyrotechnics against different species of fish-eating birds. This may be partially dependent on the availability of alternative feeding and loafing areas for birds.

Pyrotechnic rocket.

Photo courtesy of Paul Butt.

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As with gas cannons, pyrotechnics are not considered effective on large bodies of water and habituation can occur rapidly if they are used too frequently. Moreover, if they are used in large numbers they are also unlikely to be cost-effective. Habituation can be delayed by using pyrotechnics selectively — i.e. infrequently and at close range, and by varying the type of shell used (whistles, bangs, flashes). However, they can be very effective at smaller sites, particularly in combination with mobile, visual scarers, other deterrents, or by occasionally killing individual cormorants.

Pyrotechnics are often used in Israel, in combination with other techniques, in effective deterrence programmes and for effective dispersal of night roosts. It should be noted that their effectiveness may be partly due to the presence of an active human operative and, with the exception of rope-firecrackers, pyrotechnics therefore represent a fairly labour-intensive method of bird scaring.

Pyrotechnics have been used to scare cormorants at several

roosts in the Northern Po Delta in Italy, with varying results. They proved useful at smaller roosts, particularly during the initial establishment period. At a large roost (2,500–3,000 birds) established 10 years previously, a large number of pyrotechnics were deployed on several after-dark occasions, with reinforcement using a laser rifle. However, there appeared to be no clear or lasting effects in this instance; the financial costs were high and the logistics complicated, and staff motivation proved difficult during inclement weather conditions.

Nevertheless, pyrotechnics can be an extremely effective and relatively low-cost, non-lethal method of bird scaring. They are easy to operate, the risks of habituation are reportedly negligible if their use is ‘randomised’ as much as possible (i.e. applied on an ad hoc, as-needs basis at different locations) and they pose fewer safety problems than shooting. However, their use should be limited to sites away from residential areas to avoid causing a noise nuisance

and problems of public safety. They should also not be used in situations where there could be a fire hazard, such as near dry vegetation. Like gas cannons, the noises can also have negative impacts on other wildlife and humans.

4.1.1.3 Shooting to scareShooting to scare is one of the most widely used techniques for deterring cormorants at sites across Europe and elsewhere. It is one of the few techniques that is employed at all types of water body, from small to large and from inland to coastal, as well as at aquaculture facilities. There are fewer legal restrictions on the use of this technique than on shooting to kill (although non-toxic ammunition must be used near water bodies in many places), and in some countries a shooting licence and appropriate insurance may be a legal pre-requisite even for shooting blank cartridges.

Shooting to scare can be used to deter birds or reinforce the scaring effect of other deterrents, such as human presence, gas guns and pyrotechnics. It is more widely

Verey Pistol. Photo courtesy of Paul Butt. Blanks. Photo courtesy of Paul Butt.

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used than the use of pyrotechnics because live ammunition is often cheaper and more readily available. The most commonly deployed weapon is a 12-bore shotgun, although relevant certificates for such use may be required. The safest way to use a shotgun for this purpose is to fire blanks, which are available from local gun dealers. This also avoids any possibility of actions being misconstrued, of birds being injured, and of adding lead to the ecosystem.

Live ammunition can also be used, but care needs to be taken not to kill or wound birds, unless the appropriate authorities approve this. The practice of ‘peppering’ cormorants with small lead shot pellets in order to deter them is commonly considered inhumane and illegal in most places. A starting pistol can be used as an effective alternative to the use of a shotgun, although care should be taken so that others do not misinterpret this course of action.

It is also possible to purchase a variety of special bird-scaring cartridges. However, these are specially designed to be fired through a signal (Verey) pistol sleeved to 12 gauge and not through a normal shotgun. Appropriate firearms certificates may also be required for these. Furthermore, because of the noise they make and the restrictions on

possession and operation, the use of bird-scaring cartridges is probably somewhat limited.

Shooting to scare can be an effective deterrent, and it is sometimes the only option available on a river or still water to which the public have access. It has been demonstrated in a recent study in the UK that shooting to scare can reduce the number of birds present at fisheries for the duration of the shooting period and for a ‘post-treatment’ period. A large-scale experiment was undertaken involving thirteen, six-week field trials carried out over two years at a range of fishery types (including river and stillwater fisheries, stocked and unstocked sites, and fisheries with and without cormorant night roosts). The experimental design involved three treatments: control (no shooting), lethal shooting and non-lethal shooting (at the same intensity). Each six week trial was divided into three two-week phases: pre-treatment, treatment (when shooting with blanks was carried out) and post-treatment. Numbers of cormorants were then compared before and after commencement of shooting and between control and shooting sites.

The results indicated that shooting (to kill or to scare) significantly reduced the number of cormorants for both the treatment and post-

treatment phase. An average bird reduction of over 50% was reported. However, bird numbers recovered to pre-treatment levels over a period of two to six weeks. To be effective in the longer term, this means that such scaring would need to be repeated at regular intervals for as long as cormorants remained in the area. When done properly (e.g. as birds first arrive), and in conjunction with other deterrents, this can be highly effective over a long period of time.

4.1.1.4 Bio-acoustics, acoustics, ultrasonics and high intensity soundBio-acoustic deterrents are sonic devices that transmit sounds with a biological meaning — for example, recorded bird alarm and distress calls. Typically, alarm calls are used when birds perceive danger, while distress calls are used when birds are captured, restrained or injured. Both types of calls are usually species-specific and can cause members of the same species to take flight, but they may also elicit a response in other species that are taxonomically related or which closely associate with the call-producing species.

Recorded alarm calls are widely used as bird deterrents, and such biologically meaningful sounds should be more repellent and resistant to habituation than other sounds, although responses vary

‘Shooting to scare is one of the most widely used techniques for deterring cormorants at sites across Europe and elsewhere’

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between species (e.g. some species of gull [Larus spp.] are initially attracted to the noise, apparently to investigate). There are reports of the successful use of broadcast distress calls to deter some species of heron (Ardea spp.) and Night Heron. However, in trials in Italy and Israel the broadcast of Night Heron distress calls at night and early in the morning caused unacceptable disturbance to people living nearby.

Researchers have reported that locating sources of cormorant distress calls is problematic. It was discovered that some commercially-sourced distress calls trialled in Italy were actually the cries made by nestling cormorants when calling their parents. Further, it has been noted that the birds rarely seem to make distress calls anyway. Despite repeated attempts by one researcher to induce and record such sounds from injured and captured adult cormorants, and while ringing nestlings, the birds always remained silent. Nonetheless, trials have been carried out in some countries with cormorant distress calls, but the results have suggested that the technique is of short-term use only and ineffective in the longer term due to habituation. Similar reports from North America indicate that distress calls were generally found to be ineffective against Double-crested Cormorants, at least over long periods of time.

The possibility of broadcasting cormorant distress calls underwater to enhance their effect (sound propagates more effectively underwater) has been considered, but it does not appear to have been tested as yet or made commercially available.

An underwater acoustic system (‘Cormoshop’®) has recently been developed and produced commercially in France, based on the calls of the Killer Whale (Orcinus orca). Underwater loudspeakers, supported by floats situated 40 cm under the water surface, diffuse sound waves into the water to frighten cormorants when they are diving. Various frequencies have been tested and those at 90 kHz — the frequency of sounds from a Killer Whale — were found to be most effective. The manufacturers have continued to revise the frequency settings and power output to further improve the effectiveness of the device.

Initially, the ‘Cormoshop’® system was tested at commercial fish ponds in France and feedback from the pond owners was largely positive. Experience indicated that diving cormorants took flight immediately and stayed away from the protected ponds. However, the device appeared to work only on ponds where the fish density was relatively low (<300 kg/ha). At higher fish densities the system appeared to be less effective, possibly as a result of the cormorant’s dive time to catch a fish being shorter because of greater food availability. The system reportedly has no adverse effect on fish behaviour and can be reliably used under all climatic conditions. However, it requires a reliable electric power source and thus may not be applicable at more remote sites.

Units have mainly been used in France and Belgium, although they have also been deployed at sites in Italy and Germany. Initial feedback from Belgium suggests

that birds habituate to the device at extensive aquaculture facilities, and it has reportedly proved too expensive for use at such locations. The device has been used with more success at fish ponds used for recreational angling, possibly as a result of the presence of the device being reinforced by regular human disturbance.

Sonic bird scaring systems that produce a variety of electronically-produced sounds, sometimes associated with randomly-activated lights, are also available commercially. The range of loud and sudden noises they produce can frighten birds but, as they have no biological meaning, the risk of habituation is greater. With

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static systems, frequent changes in location and adjustment of the sounds produced can reduce this risk, and mobile (e.g. vehicle-

mounted) systems that can be used in response to bird problems are more effective, though they are also more expensive due to the labour

involved. Some reports suggest such devices can deter cormorants, although a proportion of the birds present were reported to dive rather than fly away.

In the Po Delta in Italy and in Sardinia, extensive trials have been conducted with sonic bird-scaring devices to scare cormorants away from their night roosts and to keep birds away from particular areas within extensive aquaculture lagoon systems where high densities of fish are held over winter. Two commercially-available devices were tested. The trials indicated that electronic sounds could be useful, at least in the short term, to deter groups of birds, but appeared to be ineffective against single birds, particularly if these birds were well used to the area. Habituation was seen as a problem and strong winds dispersing the sound away from the desired direction was also considered to have affected the efficacy of the devices.

Evidence indicates that most species of birds do not hear in the ultrasonic range (>20 kHz) so there is no biological basis for using ultrasonic devices and no evidence that such devices deter birds. Ultrasound loses intensity far more quickly with distance than regular sound, so it is usually ineffective outdoors.

High intensity sounds, such as air horns and air-raid sirens, can distress birds and cause them to leave a site. However, they have a relatively short range and birds appear to habituate quickly to their use. Trials at aquaculture facilities in Israel and Italy with vehicle horns and sirens have reportedly

Sonic bird scaring devices. Photos courtesy of Josef Trauttmansdorff and Paul Butt.

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proved largely ineffective or effective only for short periods. These devices can also cause hearing damage to humans and are generally not recommended for general use. However, sirens mounted on vehicles can provide an effective combination of human presence with an audible deterrent, and they have been used with some success in Israel to scare birds at fish farms.

Sound transmission from all sonic devices is influenced by ambient temperature, wind direction and reflections from surrounding features such as buildings, and this should be taken into account when setting up such devices. As with most methods of bird control, using such devices as part of an integrated approach with a variety of techniques is likely to be more effective and will help reduce the risk of habituation.

4.1.1.5 Other sound-producing techniquesOther sound-producing techniques can also be used to deter cormorants. For example, tapes that produce a humming or clacking sound when they move in the wind can also be used, and the combination of sound and a visual deterrent can be effective (see Section 4.1.2 on visual deterrents).

4.1.1.6 Overview of auditory deterrents

EfficacyAuditory deterrents can be effective against cormorants. The effectiveness varies with the device chosen, the method of use, the size of the site and the availability of alternative foraging sites to which the birds can relocate. Such

devices have a limited range, and this can be influenced by wind strength and direction, ambient temperature, and surrounding features such as buildings. Thus, they are most effective at smaller sites, or at particular locations at larger sites (e.g. netting stations or known predation ‘hot spots’) to address specific, local problems. All audible deterrent techniques are subject to habituation (birds learn that they pose no danger and ignore them), and hence they are more likely to be of short-term benefit, generally for weeks or shorter periods. However, efficacy can be extended considerably by moving devices regularly or mounting them on a vehicle for maximum mobility, where they are reinforced by human presence, using variable firing intervals and by employing them as part of an integrated control strategy alongside other measures.

In general, techniques such as pyrotechnics and shooting to scare appear to be more effective and longer lasting against cormorants than static devices, probably due to the reinforcing effect of human presence and, where this is used, shooting to kill, as well as the more flexible and targeted means in which they are deployed. Such measures also appear to be more effective if birds are exposed to true danger (e.g. due to shooting or if hunting is permitted) in the surrounding area.

PracticalityAuditory deterrent devices are used widely for a range of bird scaring purposes. They are readily available, relatively easy to deploy and simple to operate. Such deterrents thus rate highly

from the viewpoint of practicality for many sites. Legal constraints on the use of some of these techniques may apply and licences or permits may well be required for their operation. Local guidance and necessary approvals should thus be sought prior to using these devices. The deployment of audible deterrents should also take account of appropriate safety issues (e.g. use near members of the public or in the vicinity of sensitive sites).

In addition, there will be a need to guard against the use of pyrotechnics in situations where there could be a fire hazard, such as near dry vegetation. It might also be necessary to consider the security of the device to minimise the risk of possible theft or vandalism (e.g. by deploying the device on an island).

Many audible deterrents require some form of power source, and this may render them more difficult and expensive to deploy, and perhaps impractical, unless there is a supply of electricity or suitable batteries that can be re-charged. It is also important that such devices will operate reliably and effectively in what may be extremely variable environmental conditions.

CostsThe price of auditory deterrents varies considerably and depends on the complexity of the device itself (e.g. from simple humming tapes to relatively sophisticated automatic devices) and the operating costs. Static devices such as automatic gas cannons, bio-acoustic deterrents and sonic devices are relatively expensive, and the costs involved in trying to apply

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these over a large area are likely to be prohibitive. However, once purchased, such devices can be used over many years and running costs are relatively low.

The costs of pyrotechnics or shooting to scare are relatively low in terms of the materials, in the short term at least. However, manpower costs have to be taken into account, particularly if dedicated staff are used for bird scaring duties, and recurrent costs can be high if such deterrents are used repeatedly. Staff costs can be reduced where volunteers or local stakeholder groups are involved in bird scaring programmes.

AcceptabilityThe use of auditory deterrents for deterring birds is widely recognised and accepted. However, general considerations with the use of all auditory deterrents relate to their potential noise nuisance and their indiscriminate impact on non-target species. Auditory scarers may be socially unacceptable in residential areas, and they may also have an undesirable effect on other wildlife and humans in the area (e.g. fishermen or fish farm workers). To an extent, the level of possible disturbance can be regulated by the way these devices are used — for example, by pointing them away from houses or constructing simple straw baffles around them. It may also be wise to advertise the use of such equipment widely to anglers, or others using a site, as the loud

bang may be disturbing to those with a nervous disposition or certain medical conditions.

4.1.2 Visual deterrents

There are a number of relatively simple and inexpensive visual deterrents, mainly used for scaring birds from farmland, which can be successfully adapted to deter fish-eating birds at fisheries and aquaculture facilities.

4.1.2.1 Human DisturbanceHuman activity has been shown to be consistently effective for scaring cormorants away from fisheries and aquaculture facilities, and it is not constrained on grounds of acceptability to other people as some other techniques often are. Human disturbance is one of the most widely used techniques for deterring cormorants, particularly at aquaculture facilities and at fisheries on smaller rivers and stillwaters, and it can be conducted on foot, using vehicles or by boat. Birds can be disturbed from

specific areas either deliberately, by direct harassment, or indirectly through, for example, leisure activities or routine day-to-day activities. However, frequent or extended periods of human presence may be needed for this to be effective. Thus, options to encourage or extend incidental human presence at ‘problem’ sites might be considered.

Human presence is also a feature of many bird deterrent methods, and it should be appreciated that it is difficult to separate the effects of another deterrent (e.g. pyrotechnics) from the effects of human presence. Cormorants can habituate to human presence, particularly if this carries no perceived threat, so the simultaneous use of other deterrents is advisable.

The timing of human activity is important. Cormorants normally leave their roost before sunrise and feed most actively just after dawn, so human presence needs

Whilst some types of human disturbance will be innapropriate at fisheries,

this is a consistently effective method of deterring Cormorants.

Photo courtesy of Paul Butt.

‘Timing of human activity is important’

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to be targeted at this time. This will be easier where personnel live on, or very close to, the site to be protected, but it may still prove to be costly or impractical. Nevertheless, human presence over a reasonable period has the advantage that it will enable an accurate count to be made of the numbers of birds affecting a site and, thus, better assessment of the extent of any problem. However, it might be noted that a study in Israel showed that cormorants shifted their main feeding time from early morning — when worker presence was high — to early afternoon, when the workers went to lunch.

Although the use of a dedicated human scarer is likely to be more expensive than other visual and acoustic methods, these costs can be offset by a greater reduction in losses. Costs can be particularly high if specific working time is dedicated to this activity and other costs are taken into consideration (e.g. fuel costs for vehicles), but they can be relatively low where human presence involves volunteers (e.g. unpaid anglers or hunters). Casual scaring associated with routine day-to-day activities can also be effective and of low cost. However, as with all scaring techniques, the success of human scaring is dependent on alternative feeding areas being available.

4.1.2.2 ScarecrowsScarecrows are a traditional, widely used method for scaring avian pests. These are sometimes designed to mimic the appearance of a predator (e.g. a bird of prey), but they are most commonly human-shaped effigies, usually constructed from inexpensive materials. In general, however,

motionless devices either provide only short-term protection or are ineffective, as the threat from them is perceived, rather than real. Some birds reportedly even begin to associate the presence of scarecrows with favourable foraging conditions. In a survey of fish hatchery managers in the United States, only one of the 14 hatchery managers (7%) who commented on the effectiveness of various control techniques said that scarecrows had a high success rate against fish-eating birds; six (43%) said they had no effect.

In a survey of 13 freshwater fish farms in the Modena district of Italy, where damage from 11 fish-eating bird species was reported, the owners or managers of four farms reported that human-shaped and/or moving scarecrows had no effect, three reported success for a matter of days and only two indicated benefits lasting weeks or months.

To maximise the effectiveness of scarecrows, it is recommended that they are made to appear life-like, possess biological significance, be highly visible and have their location changed frequently to delay habituation. Fitting scarecrows with loose clothing or bright streamers that move and create noise in the wind can also enhance their effectiveness. Alternatively, scarecrows might mimic clothes worn by active human scarers. For example, dressing both scarecrows and the farmers in bright yellow raincoats with hoods and having the scarecrows ‘hold’ a black pipe (as a replica gun) enhanced the efficacy of scarecrows at an Israeli aquaculture facility. This scaring was reinforced by periodic shooting in the area,

undertaken by people dressed in similar yellow, hooded coats.

Revolving scarecrows are brightly coloured devices that spin slowly as the wind blows. Some are human-shaped, while others consist of a revolving square, sometimes painted with large predator eyes (also known as ‘hawkeye’ deterrents). Both designs can be enhanced by the addition of a mirror that flashes as the device revolves. As these devices are wind operated, there is minimal maintenance and these devices are relatively inexpensive.

There are many types of automated scarecrows available for fishery use, most of which have been adapted from scarers used in agriculture. The more sophisticated devices are powered by 12-volt car batteries, and they display and collapse on a controlled-time basis or with motion detectors. These scarecrows can also be fitted with various extras such as hooters, sirens and lights.

Scarecrow with replica gun and

dressed in yellow coat.

Photo courtesy of Simon Nemtzov.

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The most effective techniques appear to be those that simulate shooting through the use of effigies that suddenly appear from cover. One example is a model of a man with a gun that is attached to a gas cannon in such a way that the effigy appears a few seconds before the cannon is fired. This can also be used for purely visual scaring when simultaneous use of the cannon is inappropriate.

Large (around 5 m high), brightly-coloured inflatable ‘men’ have also recently been produced, primarily for advertising purposes. This type of device is powered by an air pump in the base, and it flaps and sways, both in a breeze and due to the continual flow of air through the device. The long arms also wave and flap about. The devices are thus highly visible over relatively long distances, and in the UK they have reportedly been successfully used against cormorants. A potential disadvantage, however, is that the inflatable ‘men’ require sources of electrical power with which to operate the air pumps.

One drawback is that automated scarecrows can be quite expensive to purchase and maintain, and unless the site is secure (e.g. an inaccessible island) they can be stolen or vandalised. Trials with these devices have had some success in reducing the presence of cormorants (and herons), but it is commonly reported that birds habituate to the devices quite quickly, and animated

scarecrows have been reported as ‘ineffectual’ against cormorants at some sites. Regularly changing the position of such devices is

Revolving bird scarer — ‘predator

eyes’. Photo courtesy of Paul Butt.

Inflatable ‘Scarey Man’ deterrent

(top), and inflatable ‘man’ (right).

Photos courtesy of Paul Butt and

http://www.immagoinflatables.co.uk/

skyguys.html.

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recommended to maximise what effectiveness they may have.

Both static and animated scarecrows are commonly used at aquaculture facilities and fishery sites, particularly smaller ones. The major drawback with scarecrows, however lifelike they may be, is that they do not present a threat that is sufficiently alarming to birds under most circumstances. Consequently, over a period of time, birds learn that effigies do not represent an actual threat and begin to ignore them. To increase the threat and therefore lengthen the time before habituation, it is recommended that all these devices are moved regularly, rather than left in one place. Moreover, devices should not be left in place once cormorants migrate from an area because, when the birds return, the period of habituation can be particularly short.

The effectiveness of scarecrows can be reinforced with other sound-

producing or visual deterrents, or, to improve effectiveness, by periodic human activity, especially if they are dressed like the scarecrows.

4.1.2.3 Predator modelsModel raptors deter birds by mimicking real birds of prey and creating fear and avoidance behaviour in the target species. Many potential prey species react to predator models. However, the strength of the response varies between species, and model raptors fail to incorporate behavioural cues, which may be critical to the induction of fear and avoidance in the target species. Model birds of prey are reported to be effective at scaring cormorants at some sites. However, there is evidence that the avoidance response to large avian predators is, in part, a learned behaviour. This may diminish the potential for the wider application of this technique against cormorants, since its main avian

predator across Europe, the White-tailed Eagle (Haliaeetus albicilla), is absent from many areas where cormorants are present.

The flying of live, trained birds of prey across bodies of water by a falconer might also be used. This has been tried in Israel. However, although its efficacy was relatively high, the farmers stopped using the birds due to the very high cost.

While most raptor models are inexpensive and easy to deploy, cormorants can rapidly learn that the model poses no threat, become used to its presence and no longer react. The deployment of a Peregrine Falcon model adjacent to cormorant feeding areas in the southern Po Delta, Italy, appeared to be largely ineffective and tends to support this view. Thus, the effectiveness of such models is increased if they can be made to look lifelike, are animated and moved frequently.

Another form of predator model that has been used is that of tethered floats made to resemble the head of a crocodile or alligator. These floats are distributed around the pond and purportedly can deter water-birds from landing on the pond. It is not known whether these have been used successfully against cormorants.

Mobile scarecrow dressed identically to local workers and also incorporating

an auditory deterrent device. Photo courtesy of Paul Butt.

‘Model birds of prey are reported to be effective at scaring cormorants at some sites’

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4.1.2.4 Displaying corpsesThe deployment of replicas or actual dead individuals in a manner which signals danger to members of the same species can be used as a visual deterrent for many bird species, especially crows (‘corvids’). Reportedly, corpses have to be in good condition to remain effective and, as with other static deterrents, they should be moved frequently to reduce habituation. Efficacy depends on the availability of alternative foraging sites and is enhanced when it is reinforced with additional deterrent techniques. While this technique is reportedly highly effective for corvids and there is some evidence it has been effective against egrets (Egretta spp.), it is not clear whether or not it deters cormorants.

The desirability of displaying corpses in areas accessed by the general public may also need to be taken into consideration in case the corpses raise public concern and complaints. There are also other considerations if real corpses are used, notably because of possible pollution arising from decomposition, particularly in fish farm areas, and health and safety fears about the possible spread of avian ‘flu.

4.1.2.5 BalloonsHelium-filled balloons are used as an inexpensive method of bird deterrence in agriculture. Their effectiveness can be enhanced by the inclusion of eyespots, consisting of a circular pattern that resembles the general appearance of vertebrate eyes. Two circular eyespots arranged horizontally, each containing concentric rings of bright colour, appear to be the most alarming and effective designs. Those that have a

three-dimensional appearance may further enhance the effect, and large eyespots are considered better than small ones. Although easy to set up and move around, balloons can be easily damaged in high winds and can deteriorate in sunlight, leading to a loss of helium and thus height. Balloons also need to be checked regularly to ensure they cannot break free from their moorings and present a hazard to aircraft. Their use near aerodromes may be restricted by air navigation regulations. A cheaper alternative is to fill the balloons with pressurised air and to hang them from T-shaped poles.

Balloons, and other visual scaring devices, have been used against cormorants to increase the deterrent effect of other physical exclusion devices such as wires and floating ropes (see 4.2).

Studies indicate that the effectiveness of balloons at scaring birds varies between species, the eyespot design and with the mode of presentation. However, effects are commonly only short-term and birds quickly habituate to them. In some places where hunting takes

place, such balloons have been used as opportune targets and their use to help deter cormorants has had to be abandoned.

4.1.2.6 KitesKites and kite-hawks are commercially available, airborne devices that are meant to act as mobile model predators which ‘target’ birds perceive as a threat. Kites commonly bear an image of a soaring raptor and are tethered to the ground. Some varieties are secured to a length of line (commonly about 80 m), but these only operate in a wind and, once grounded, have to be re-launched manually. Alternative models are tethered to a flexible 13 m pole and re-launch automatically when the wind starts blowing. The ‘Helikite™’ is a cross between a large helium balloon and a kite, which ‘flies’ above a pole. This has the advantage that it does not need wind to stay in the air.

Like balloons, kites and kite-hawks can be damaged by strong winds and may be difficult to keep up in the air when wind speeds exceed 8 km/hr. Since they pose no real

Raptor kite. Photo courtesy of Paul Butt.

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threat to birds, do not behave like raptors, and remain visible for long periods, birds quickly habituate to these devices. Hence, they are effective only over a small area and for a short period of time. As with balloons, their use near aerodromes may be controlled by air navigation regulations.

4.1.2.7 Radio-controlled model aircraftRadio-controlled aircraft have been used to scare bird pests since the early 1980s. Although mainly used over airfields, this technique has also been applied at other sites, including deterring cormorants and herons at fisheries and aquaculture facilities. For cormorants, experience has shown that model aircraft should be used to scare birds while they are still in the air, as birds already on the water are only encouraged to dive. At larger, land-based fish farms it has been estimated that one model aircraft is required for approximately every 100 ha. Using a falcon-shape aircraft, or a conventionally shaped aircraft painted with a raptor design, can enhance the efficacy of this technique. While quite effective, the use of model aircraft is relatively expensive, labour-intensive, not suitable in bad weather and requires skilled operators — training to become fully competent can take up to two months

In Finland, an attempt to scare cormorants was made using a small, wind-driven helicopter rotor mounted on a tripod. Although the efficacy of the device was not fully monitored, it is thought to have been partially successful.

4.1.2.8 LightsFlashing, rotating, strobe and searchlights are a novel stimulus to

birds and can produce an avoidance response. Lights may be relatively ineffective during daylight hours but they may be particularly useful for deterring night-feeding birds such as herons, or at night roosts. They are easy to deploy and require very little maintenance, but birds will quickly become habituated and so lights are best used in combination with other deterrent methods. They should not be deployed where they might cause a visual nuisance to neighbouring properties or near airfields.

4.1.2.9 Mirrors/reflectorsMirrors and reflectors work on the principle that sudden bright flashes of light produce a startle response and so drive birds from an area. For example, CD discs are highly reflective and can be hung on wires or other objects where they will move with the wind to deter birds. Rotating, reflective pyramids have also been developed that are powered by a 12-volt battery and deflect light into the air at the angle of the birds’ approach. These automatically switch off in the dark and will run for several weeks between battery changes. Although inexpensive and easy to put up and relocate, the effectiveness of mirrors and reflectors as a bird scaring technique is variable.

In a survey of 336 fish hatchery managers in eastern USA, eight reported using tin reflectors of which seven said they had limited

or no success as a depredation control technique. However, it is known that reflectors can be effective at deterring cormorants at some sites, particularly in sunny locations. For example, in Israel, hand-held mirrors are reported to be very effective. As with many other deterrent techniques, they are best combined with other methods of scaring. For instance, on a large lake in Greece, mirrors and audible deterrents have been used successfully to deter cormorants from sites close to the shore (see Case Study No. 1).

4.1.2.10 Reflective tapeTapes can best be regarded as a combined visual and exclusion deterrent (see Section 4.2.2). A wide variety of twines and tapes are readily available, including varieties such as Mylar® Tape, which has a metal coating on one side that reflects sunlight and also produces a humming or crackling noise when moved by the wind. Tapes are relatively cheap and easy to deploy, but they can break easily in bad weather conditions, necessitating extra labour for repairs and, potentially, causing an unsightly litter nuisance. Good maintenance of the tapes is essential in order to stop gaps resulting from broken tapes being exploited as entry points by birds. Strips of reflective tape are often hung from wires that are stretched across fish ponds (see Section 4.2.2) to make the wires

‘Lights may be relatively ineffective during daylight hours but they may be particularly useful at night roosts’

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more visible and to increase their effectiveness as deterrents.

Reflective tapes are in regular use at aquaculture facilities in a number of countries (e.g. Germany, Italy and UK), and close configuration of these tapes can provide successful protection, particularly if an alternative feeding area is available nearby. However, since the tapes are short-lived, the technique is probably best suited to protecting small areas of high value stock in the short term.

A cheap source of reflective tape is the magnetic tape in old video cassettes, since this is highly reflective and easily available. However, it is inadvisable to use tape from video cassettes with a play length of longer than two hours, as these are made of thinner (and more breakable) tape.

4.1.2.11 Flags, rags and streamersFlags, rags and streamers, including reflective silver or Mylar® streamers, can be readily deployed at fishery and aquaculture sites and — potentially — also at roost sites. These are cheap and easy to deploy and can prove effective deterrents, in the short term at least. Their success depends on alternative feeding, roosting or loafing sites being available nearby.

4.1.2.12 LasersAs the demand for non-lethal, environmentally safe methods of bird scaring has increased, there has been increasing interest in the use of lasers to scare birds. Lasers, particularly ones that work under low light conditions, are an attractive alternative to other bird scaring devices since they are silent and can be accurately

directed over distance on specific problem birds. Birds are startled by the strong contrast between the ambient light and the laser beam, by the bright spot moving toward them on the ground or in the tree and by the actual beam when it reflects dust particles and appears as a large ‘stick’ moving toward them. The laser light need not be shone into the bird’s eyes to startle them, and indeed it is inadvisable to do so. During low light conditions this technique can be applied very selectively, but at night the light beam is visible over a large distance and hence can cause non-selective disturbance. These devices are ineffective in daylight and in misty or foggy conditions.

The possession and use of lasers may be prohibited or restricted by legislation or be subject to a licensing regime, depending on the power of the laser being deployed. There are growing safety concerns regarding the availability and use of lasers and calls for tighter regulation in some countries. Thus, the legal aspects of using this technique should be checked with the local authorities before any laser devices are considered for deployment: laser devices should only be used within the limits of appropriate laser safety regulations.

From a safety point of view, shooting a laser light must be regarded the same as shooting a bullet — the operator MUST be

sure of the precise target and what the end of the beam will hit. Some lasers can be dangerous at short or even large distances, and proper training and adherence to local laws is essential. Lasers can blind people or animals, permanently or temporarily, and this can also lead to unexpected accidents (e.g. car crashes) if devices are used inappropriately.

Trials with low power (5 mW) red laser (650 nm) guns, such as the Desman rifle®, in France, Italy and the UK have demonstrated that cormorants are sensitive to this laser light and that these devices can be effectively used at cormorant roosting sites. In

one trial in the UK, conducted during cloudy weather, most of the cormorants at a night roost were scared away within 20 minutes, and treatment over consecutive evenings caused the temporary desertion of the roost.

In similar trials in roosts in the northern Po Delta, Italy, birds left the roost almost immediately. In Italy, lasers have been successfully used against birds in both tree roosts and bankside areas, sometimes hundreds of metres from the bank- or boat-based operator. The gun ‘scope’ on laser guns proved useful to accurately target the laser light, and the use of a light amplifier also helped to enhance the efficacy of the device

‘Birds are startled by the strong contrast between the ambient light and the laser beam’

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in the dark. It was reported that lasers were particularly effective at preventing the establishment of new roosts, especially when used in conjunction with shooting to scare techniques.

Similar findings have been demonstrated at other cormorant night roosts, although in some trials the laser gun has been less effective, with some birds failing to leave the roost site (e.g. if the bird is facing away from the light source), thereby discouraging other birds from leaving, too. This reinforces the desirability of deploying a mixture of cormorant scaring devices and techniques.

Laser guns are available commercially for avian deterrence (e.g. Desman rifle®, Avian Dissuader), and some manufacturers also provide training in their use. Other, automatic laser devices have been developed for deterring birds, particularly near airfields to reduce the risk of ‘bird strike’. However, these devices are relatively expensive. Due to concerns about the safety of such devices for humans, one commercially available laser gun was tested for safety at the UK Government’s Defence Evaluation and Research Agency (DERA). This was found to be safe if it was not pointed at an unprotected human eye within a distance of 155 m, although the safe distance was considerably reduced if viewed with binoculars.

Green lasers (530 nm) are also available and tend to be brighter than red lasers of the same power level. Green lasers are being sold commercially as laser guns for bird scaring, but these are as

expensive as the red laser guns (above). However, low-cost, hand-held green laser pointers are also available with a wide variety of power levels, and these have been used successfully for bird scaring at night roosts in Israel and Italy. Low power lasers of less then 5 mW have fewer legal restrictions, though these can potentially still cause eye injuries, and can be effective at ranges of up to a few hundred metres. Green laser pointers of 20–30 mW are effective over larger distances (1–2 km), but usually carry more stringent legal restrictions and safety standards than the 5 mW lasers, reflecting the greater risk that they pose. Green laser pointers of 50, 100 or even 200 mW are also available, but these are increasingly dangerous and apparently no more effective in scaring birds than the less powerful ones. It is anticipated that further controls are likely to be placed on the availability and use of lasers and thus particular care is needed to ensure compliance with local regulations, as well as to ensure safe usage where this is appropriate.

4.1.2.13 High-Pressure Water JetsHigh-pressure water jet systems have been successfully tested on Carp ponds in Germany. Aside from deterring predators and making the fish less accessible, a positive side-effect of this technique is that the ponds are also aerated, an important benefit during summer when the dissolved oxygen in Carp ponds can fall to very low levels.

A similar device has also been used in Sweden for protecting circular fish ponds from gulls and terns (Sterna spp.). This rotating device

had four arms that sprayed a mist of water over the ponds, reducing visibility and preventing birds from seeing the fish. The spray also provided shade by diffusing direct sunlight, and oxygenated the water. The latter technique was not tested against wading or diving birds, but both methods may be useful to deter cormorants, particularly at smaller ponds on fish rearing sites. The potential for their use in protecting larger, irregular water bodies may be limited because of the cost and the practical installation difficulties.

4.1.2.14 Dyes, colourants and turbidityThere has been little research into the use of dyes or colourants to deter fish-eating birds, but it is known that cormorants are visual feeders, in part at least, and that birds can abandon feeding sites in response to changing water quality conditions such as turbidity (i.e. reduced water clarity). Studies have also indicated that the foraging efficiency of egrets was reduced by increasing the turbidity in trial ponds (obtained by dilution of natural sediment). Thus, some researchers have suggested that such measures might represent a cost-effective method for protecting stocks at fish farms or in ponds and small lakes, since these could be relatively easy to apply in such small, confined water bodies. In practice, such an approach may conflict with fish husbandry practices in fish farms (and perhaps feeding of the fish).

Equally, the practice of deliberately increasing turbidity at a site may be questionable from an acceptability viewpoint on biodiversity/aesthetic grounds, although the

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presence of benthic (i.e. bottom feeding) species such as Carp at fisheries often has this side-effect, particularly at small stillwater sites where stocking rates are high. The potential for using dyes or artificially manipulating turbidity as a cost-effective method of cormorant control has yet to be proven.

4.1.2.15 DogsTrained dogs, such as border collies, can be used to scare birds away from a site. The efficacy of such an approach for deterring cormorants is not known.

4.1.2.16 Overview of visual deterrents

EfficacyAs with auditory deterrents, the effectiveness of visual deterrents varies with the device chosen, the method and timing of use, the size of the site and the availability of alternative foraging sites for the birds. Typically, fixed visual deterrents are only thought to have an effective range of up to about 200 m. As such, these techniques will be of limited, if any, use on river systems, coastal areas or larger stillwater sites, with the possible exception of localised predation ‘hot spots’, or in the vicinity of fishing gear.

All visual deterrents, particularly static ones, are subject to habituation by cormorants, and hence they are generally of short-term benefit (typically days to weeks) as the birds eventually get used to them, unless they are moved regularly and used in conjunction with other deterrents. The effectiveness of visual deterrents also depends on their

visibility and how real a threat they are perceived to present: visual scarers are most effective if they are life-like, move and possess biological significance, or if they are associated directly with a real threat.

Disturbance by humans is regarded as the most effective visual deterrent, but cormorants can learn to feed during even short periods when humans are absent (e.g. meal breaks), especially where feeding success can be assured (e.g. at heavily-stocked fish ponds). Studies suggest that human effigies and raptor models may be more consistently effective and longer lasting as bird deterrents than kites, balloons and flags.

PracticalityVisual deterrent devices are used widely for a range of bird scaring purposes and most are readily available, easy to deploy and simple to use. Such deterrents thus rate highly from the viewpoint of practicality for many sites. Regulations may cover the use of some visual deterrent devices (e.g. lasers, model aircraft, flashing lights) and/or restrict their operation in sensitive areas such as airfields. Local guidance and necessary approvals should always be sought prior to using such devices. For more expensive visual deterrents (e.g. automated inflatable scarecrows), security should be considered carefully to safeguard the devices against theft or vandalism.

CostsThe costs of visual deterrents vary widely, depending on the complexity of the device itself and the level of human participation

required. Simple static scarecrows and flags are usually constructed from inexpensive materials, while automated devices are relatively more expensive, depending on their level of sophistication, and devices such as some lasers can be costly. Commercial bird-scaring laser guns can be very expensive, but cheaper, hand-held laser pointers can be just as effective. Laser licensing and training costs must also be taken into account.

For many visual scarers, manpower costs are low, being mainly confined to initial deployment, periodic checking and, perhaps, movement around a site. However, the cost of using dedicated staff for ‘human disturbance’, or to operate a laser gun, may be considerable, particularly if required on a regular basis. Manpower costs might be reduced where incidental human presence at a site can be arranged or where volunteers or local stakeholder groups participate (see Case Study No. 4 — Slovenia).

AcceptabilityThe use of visual deterrents for scaring birds is widely recognised and, since their impact is usually very localised and non-lethal, they have a high level of acceptability and are generally not a matter of public concern. However, such devices are not selective and so may impact on other wildlife, and this should be taken into account. Some visual deterrents may not be acceptable in certain locations (e.g. flashing lights or perhaps bird corpses near residential areas, model aircraft and kites near airfields, or lasers near roads). Particular care is also necessary with all uses of lasers even where it is legal to use them.

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4.1.3 Chemical deterrents

Chemical taste repellents are quite widely used for reducing the impact of pest birds in agriculture and forestry, as well as a means of deterring birds from perching on buildings. Such techniques have not been widely tested against fish-eating birds, but they may have some potential. Chemical repellents fall into two broad categories: primary repellents and secondary repellents. Primary repellents are avoided upon first exposure because they smell or taste offensive or cause irritation. Secondary repellents are not immediately offensive, but they cause illness or an unpleasant experience following ingestion. The bird links this negative experience to the taste of the treated food and will avoid this food in future. Due to their toxicity, and concerns about adverse effects on the environment, the use of chemical repellents is usually tightly regulated.

A number of chemicals (such as methyl anthranilate, dimethyl anthranilate, cinnamide, anthraquinone, adirachtin, 4-aminopyridine, methiocarb, and caffeine) have been proven as effective deterrents against different bird species. Some of these substances are registered as bird repellents in the USA, but they are not authorised for use in many other countries and few chemicals are believed to be registered for use in Europe. In addition, not all of them have been tested on cormorants.

Chemical repellents are generally most effective on surfaces or indoors, and animals usually habituate to smells quickly. For

these reasons they are difficult to apply effectively outdoors, especially in large areas such as fish growing areas. In addition, most are relatively expensive. Furthermore, methyl anthranilate can be toxic to aquatic fauna and may not be sprayed near water bodies unless it is in a special formulation designed for this purpose.

Despite these drawbacks, chemical repellents have been used effectively to deter birds, including cormorants, from large areas, such as airports. The repellents are typically applied using a fogger machine; in some places the foggers have been attached to motion detectors so that they only spray chemical when flocks of birds approach, to avoid habituation and to reduce costs. The potential of applying repellents as a very thin surface film, in order to deter birds from entering particular water bodies, has also been investigated. Research in this area is believed to be ongoing.

Most bird deterrent chemicals do not impact mammals, and mammal deterrents such as hot-sauce (capsaicin) are ineffective against birds due to differences in their nervous systems. Nevertheless, many people dislike the smell of some of these chemicals, especially the sickly-sweet, grape-like smell of methyl anthranilate, so it should not be sprayed near settlements.

Trials have also demonstrated that conditioned taste aversion (a subconscious association between taste and a feeling of illness experienced after ingesting treated food) can be successfully induced in captive cormorants fed on dead fish dosed with carbachol.

Individual birds learned to avoid Brown Trout (Salmo trutta), the treated species, but continued to eat other species of fish, and this effect lasted for seven months - the entire duration of the trial — without reinforcement.

Clearly, applying such a technique in the wild presents significant difficulties and would not be appropriate at sites on cormorant migration routes, due to the extensive turnover of the birds. However, it might have potential at some sites where birds demonstrate local feeding-site fidelity and where there is a need to protect a particular species of fish. Considerable further work would be required to develop an effective method for delivering the chemical to the target birds.

Because of the complexity and drawbacks of using chemical repellents for deterring birds outdoors, and the associated controls on their use, it is important that all aspects, potential repercussions and regulations are considered carefully before commencing any programme to use them against cormorants.

4.1.3.1 Overview of chemical deterrents

EfficacyThe efficacy of chemical deterrents will be highly variable depending on which chemical is used on which species and on the mode of delivery. While proven to be effective for captive cormorants fed on dead fish, safe and effective chemical repellents have not been developed to a level where they can be recommended for use in fishery or aquaculture applications at the current time.

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the intercafe cormorant management toolbox

PracticalityChemical deterrents are most effective on surfaces and in enclosures, and they are more difficult to apply outdoors. The practicalities of administering repellents to cormorants and/or water bodies require considerable further work before the technique could be recommended for wider use.

CostsMost chemical deterrents are expensive, although fogging machines can reduce the amount of chemical needed. However, in large areas the costs can be prohibitive.

AcceptabilityChemical deterrents that do not harm (but only deter) wildlife are generally very acceptable as a non-lethal method to stakeholders. However, the use of potentially harmful chemicals in the environment does raise acceptability issues and requires mechanisms to ensure that substances could be administered to cormorants without a risk of lethal poisoning, or threatening other bird and other, non-target wildlife species. Thus, any possible human health or environmental implications would have to be taken into account to ensure any such techniques did not have adverse effects.

4.2 Protecting The Fish — Exclusion Techniques

These tools involve excluding the birds from the fish. Not surprisingly, the techniques work best when fish are concentrated in relatively small areas. Thus, they are ideal for land-based ponds or raceway fish farms where netting enclosures can be

fixed permanently. At other sites, such as off-shore fish farm cages, anti-predator netting can be hung in curtains underwater to prevent diving birds reaching fish stock in the mesh ‘bag’ of the cage. In larger water bodies, complete exclusion is far more difficult and may well be impractical. At such sites it may be possible to take advantage of the fact that cormorants generally require quite long distances for take-off and landing. By positioning wires or ropes across waters it may

be possible to make it difficult, or impossible, for cormorants to land on, or take off from, the water’s surface. Although certain spacings of these wires appear to be more effective than others, there is considerable scope for experimentation at fishery sites.

4.2.1 Netting enclosures

Complete enclosure of a site with netting is undoubtedly the most effective option for preventing predation by fish-eating birds,

Netting enclosures at fish farms.

Photos courtesy of Bruno Broughton and Thomas Keller.